The present invention relates generally to sealing a moveable member with respect to a fixed member and, more particularly, to a pressure responsive sealing system for inhibiting leakage of high pressure fluid from a working chamber of a hydraulic actuator.
Hydraulic actuators, such as shock absorbers, are used in connection with automotive suspension systems to absorb unwanted vibration (impacts, loads, etc.) which occurs during operation of the motor vehicle. To absorb the unwanted vibration, shock absorbers are generally connected between the body and the suspension of the motor vehicle for generating a damping force in response to relative movement therebetween. This damping force acts to counteract the unwanted vibration which would otherwise be transmitted from the suspension to the vehicle body. As is known, the greater the degree to which the flow of damping fluid within the working chamber is restricted by the piston valving, the greater the damping forces which are generated by the shock absorber.
Conventionally, shock absorbers have a seal member disposed between an upper end cap of the shock absorber and the piston rod for preventing damping fluid from leaking to the outside of the shock absorber upon reciprocal movement of the piston rod. Typically, these seals have a plurality of annular lips which engage the piston rod to prevent damping fluid from flowing therebetween. While such seals are generally effective in preventing leakage of damping fluid from the working chamber to the exterior of the shock absorber, suspension component manufacturers are continually working to improve the reliability and cost of sealing systems.
More particularly, in those suspension applications using high pressure hydraulic actuators to generate a lifting force for leveling the vehicle body, conventional seals tend to leak when the vehicle is stationary for an extended period of time. Moreover, conventional seals generate relatively large frictional forces between the piston rod and the seal member which must be overcome during operation of the shock absorber.